Lab 15 Environmental Factors

What are types of environmental factors affecting the growth of microbes?

• oxygen

• temp

• pH

• osmotic pressure

• ultraviolet light

What are 5 oxygen requirement classifications?

1. Oblique aerobes

2. Facultative anaerobes

3. Aerotolerant anaerobes

4. Microaerophiles

5. Obligate anaerobes

Obligate aerobes

require oxygen for respiration

Facultative anaerobes

grow in presence of absence of oxygen

can do aerobic and anaerobic respiration

Aerotolerant anaerobes

do not require oxygen but are also not negatively affected by it

Microaerophiles

survive in environments that contain less than atmospheric oxygen levels

Obligate anaerobes

even small amounts of oxygen are lethal

What does the fluid thioglycollate medium test for?

Test for the aerotolerance of microbes

What is the indicator of Thioglycollate Medium? How does it work?

Resazurin — O₂ indicator

Turn pink when oxidized and colorless when reduced

What is the result Thioglycollate Medium if the organism produces an oxygen gradient from fully aerobic at the top to anaerobic at the bottom?

Fresh media appears straw colored with a pink region at the top where the dye has been oxidized

T/F: Small amount of agar in Thioglycollate medium slows the oxygen diffusion

True

T/F: Upon autoclaving, oxygen is removed and diffuses back into the medium as the tube heat up to 60 degrees

False, the tube cools down to room temperature

Resazurin turns pink

meaning…

Resazurin has been oxidized

Resazurin remains colorless

meaning…

Resazurin has been reduced

What this Thioglycollate result tube indicates?

Confluent growth throughout the tube

→ Aerotolerant anaerobe

What this Thioglycollate result tube indicates?

Growth throughout the tube, but the growth is denser towards the top

→ Facultative anaerobe

What this Thioglycollate result tube indicates?

Growth in center of tube, but not at the top or bottom

Microaerophile

What this Thioglycollate result tube indicates?

Growth only at the top of the tube

Oblique aerobe

What this Thioglycollate result tube indicates?

Uninoculated control tube

What this Thioglycollate result tube indicates?

Growth only at the bottom of the tube

Obligate anaerobe

Describe the cardinal temperature of each bacterial species

• bell curve shape with minimum and maximum temperature with the lowest growth 

• the tip is optimum with the highest growth

What are some thermal classifications of bacteria?

• Psychrophiles

• Psychrotrophs

• Mesophiles

• Thermophiles and Hyperthermophiles

Grow only below 20 degrees

Temperatures are always cold

Do not fluctuate

Psychrophiles

Which temperature class is common in ocean, arctic, and Antartic habitats?

Psychrophiles

Adapted to cold habitats that fluctuate from 0 - 30 degrees

Psychrotrophs

Grow between 15-45 degrees

Includes most human pathogens and mammalian commensal bacteria

Mesophiles

Grow at temperatures above 40 degrees

Thermophiles

Obligate thermophiles

Will not grow below 40 degrees

Facultative thermophiles

Grow optimally above 40 degrees but will grow below

What are major classifications of optimal pH survival?

• Acidophiles

• Neutrophiles

• Alkaliphiles

T/F: Bacteria live in habitats across pH spectrum. Each can survive in a wide range of pH

False, the range of an individual is small

Why does bacteria have to maintain the internal pH at nearly neutral range despite of their environmental pH?

Because change in internal pH can cause damage to vital enzymes

Adapted to grow well below pH 5.5

Acidophiles

Prefer pH levels between 5.5 - 8.5

Neutrophiles

Live above pH 8.5

Alkaliphiles

What is the concentration of water in cell?

80-90%

What is osmotic pressure?

The amount of pressure required to prevent water from passing through the cell membrane by osmosis

Osmosis def

Movement of water through a cell membrane from low salt concentration to high salt concentration

If cells are in a hypertonic environment ( higher salt M. outside)

Cells will ___

shrink because water will leave

desiccation

If cells are in an isotonic environment (equilibrium salt M.)

Cells will ___

nothing

water come in and out balance

If cells are in a hypotonic solution ( low outside salt M.)

Cells will ___

lyse

water come in and burst the cell open

Which type of solution is used to prevent soilage of food products?

ex: Sugar in jelly, salt on meat

Hyperosmotic solution

T/F: Microbes tend to have a distinct range of salinities which are optimal for growth, but they can tolerate outside the range

False, they have little to no growth outside the range

Grow optimally at NaCl con. of 3% or higher

Halophile

Require NaCl conc. of 15-25%

Extreme halophile

Will grow at salinity conc. over wide range.

Most live where NaCl conc. are 3% or less

Osmotolerant

Which class of osmotic stress bacteria that lives in ocean water

Salt conc = 3.5%

Halophile

Which class of osmotic stress bacteria that lives in dead sea or brine vats?

Extreme halophile / obligate halophile

Which class of osmotic stress bacteria that lives on our skin?

Osmotolerant / facultative halophile

Does UV light have higher or shorter wavelength than visible light?

shorter because it is stronger with higher frequency

Which type UV light that has wavelength range 315-400 nm?

UV A

Which type UV light that has wavelength range 280-315 nm?

UV B

Which type UV light that has wavelength range 100-280 nm?

UV C

What is the germicidal wavelength of UV C light?

254nm

Why does UV light can be used as a germicidal agent?

Because UV radiation can damage to DNA by thymine-thymine dimers

Prohibiting reproduction

How do endospores survive 5-50 times better in UV exposure than vegetative cells?

Because the DNA is protected inside the protein walls, preventing formation of thymine-thymine dimers

DNA is repaired prior to germination

What is an example of bacteria that form endospore and survive up to 6 years in space ( longest record)

B. Subtilis